Measuring and testing – Sampler – sample handling – etc. – Flow divider – deflector – or interceptor
Reexamination Certificate
1999-08-09
2002-03-19
Noland, Thomas P. (Department: 2856)
Measuring and testing
Sampler, sample handling, etc.
Flow divider, deflector, or interceptor
C073S863610, C073S865500
Reexamination Certificate
active
06357305
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns a process for sampling disperse material flows in which, within a process mainstream, an analysis substream is taken from said process mainstream for subsequent analysis, and an apparatus for the performance of this process.
The size distribution of the particles or droplets, hereinafter referred to generally as particles, is of considerable importance for the production of disperse solids and emulsions as it essentially determines the reactivity, transport properties and stability of the material system.
Consequently, knowledge of the particle size distribution (PSD) enables the production process to be optimised and production to be geared to the required quality. To this end, an apparatus for determining the particle size distribution is necessary which can be integrated with ease at various points in the process without causing any noticeable disruption to the process sequence.
Devices for determining particle size distributions have long been well known and employ various measuring principles. In many applications, there is an increasing trend towards devices based on laser diffraction (LD) as this combines high measuring accuracy with good stability of the results, short measuring times, a wide measuring range, a low measuring range bottom limit and easy handling.
These devices utilise the fact that a particle irradiated by a monochromatic, coherent light deflects portions of this light with different degrees of intensity depending on its size, with small particles deflecting the light more intensively than large particles. This deflection of light is known as diffraction.
In a normal arrangement according to
FIG. 1
, a laser
1
followed by a divergent lens system
2
generates a dilated, parallel measuring light beam which illuminates particles
8
introduced into a measuring cell
7
. The diffracted light is directed by a convergent lens
14
, the Fourier optical system, onto a photodetector
16
with a multiplicity of elements which, together with a downstream electronics unit, enables the intensity distribution to be precisely mapped. The particle size distribution can then be calculated from this intensity distribution by means of an evaluation unit
20
using known algorithms.
Such an apparatus is equally suitable for determining the particle size distribution of disperse solids, suspensions and emulsions. Known calculation methods based on the Fraunhofer diffraction, yield a particle size distribution irrespective of the optical properties of the particles and those of the surrounding medium.
The suitability of these devices is, however, limited to the range of low particle concentration as operations are preferably performed by transmitted light and the measuring zone must allow the diffracted light to pass through. Moreover, the particle concentration must be kept sufficiently low so that the diffracted light is not diffracted again at downstream particles. This latter phenomenon, known as multiple scattering, can be taken into account when calculating the particle size distribution. The known algorithms for this purpose are limited to special particle forms and require precise knowledge of the optical parameters of the material system, a knowledge that is usually absent in relation to most particles.
The high mass flow rates which are usually encountered in production processes, often amounting to several tons per hour, therefore mean that it is necessary as a rule initially to remove from the process a sample or specimen and to reduce the particle concentration of this sample by addition of the medium surrounding the particles, i.e. by dilution, so that the maximum permissible particle concentration in the measuring zone is not exceeded. This process is only permissible for those material systems in which dilution does not alter the particle size distribution.
The sample in such cases has to be taken in a manner which ensures that the particle size distribution of said sample corresponds to the particle size distribution of the process in the time window under consideration, i.e. such that it is representative. This in turn requires that all areas of the transport cross section are equitably sampled and that the removal of the sample does not change the particle size distribution at the sampling location. If the process particles are incorporated in a flowing medium, then it is well known that the sample has to be removed isokinetically, i.e. that the particles are not allowed to undergo any velocity change as otherwise the particle size distribution of the sample would be noticeably altered as a result.
It is also well known in relation to laser diffraction that agglomerated particles are determined on the basis of their agglomerate diameter. In normal applications, it is the particle size distribution of the primary particles which is of primary interest. The agglomerated particles first have to be separated before they pass through the measuring zone. Various devices are known as being capable of performing this task, termed dispersion, which separate the dry particles in flows of high turbulence by causing the particles to impact against one another or to impact against the walls, or which use specifically introduced obstacles or apply centrifugal forces so that the particles become separated as a result of velocity gradients. Devices are known for suspensions in which a liquid, in some cases assisted by special chemical substances and the application of ultrasound, is used to separate the particles.
In order to eliminate from the calculated particle size distribution fluctuations in the optical properties of the components, e.g. the laser, and fluctuations in the efficiency of the Fourier optical system due to the presence of particles, from time to time a reference measurement is necessary in which the intensity distribution of the medium surrounding the particles is measured in the absence of particles.
Various devices have been proposed for determining particle size distributions within the process, but these only meet the indicated requirements in part, and usually only with considerable restrictions.
In the simplest known type of device, the laser diffraction system, is directly flanged onto the process piping, i.e. the entire process mass flow has to pass through the measuring zone. The high optical concentrations which occur in this case are adjusted on the basis of a material-dependent correction of the multiple scattering pattern. A reference measurement is only possible prior to commencement of a production phase (batch). The light source and detector are kept extensively clean by gas-purged tubes or by an enveloping flow passing along windows. Any contamination of the lens system which still occurs therefore falsifies the results in a protracted manner. Dispersion of the particles does not occur. Such a device is therefore only suitable for very small pipe diameters with production mass flow rates in the range of a few kg/h and where production times (batch times) are short. The analysed sample is rendered non-representative in its definition by the geometry of the measuring zone and the laser beam profile.
In another device, the light source and detector unit are integrated in a rod with an aperture transverse to the rod longitudinal direction, which is immersed through a flange into the process mass flow. The limitations of the above-mentioned type are extended by this non-representative sampling method, with particular problems being encountered in the case of this device with regard to keeping the windows clean.
In a further development, the first-mentioned device type is implemented with static, non-representative sampling in the bypass to a pipe of larger cross section. Sampling is performed at a fixed, definable position in the process pipe. Sample transfer is performed by a jet pump which further dilutes the analysis substream and is adjusted so that the sampling operation is performed as isokinetically as possible. The sampling tube is permanently open and exposed to the abrasive pr
Röthele Stephan
Witt Wolfgang
Dilworth & Barrese LLP
Noland Thomas P.
Sympatec GmbH
LandOfFree
Method and device for sampling dispersed streams of material does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for sampling dispersed streams of material, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for sampling dispersed streams of material will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2868214